Polymerisable composition and the use thereof

ABSTRACT

The invention is directed to compositions containing at least one olefinic monomer, at least one polymer prepared form an olefinic monomer, an indicator dye to the basic structure of which an olefinic polymerisable group is covalently bonded directly or via a bridge group, at least one diolefinic cross-linking agent, and an effective amount of a polymerisation initiator; to polymerisates of the compositions, the polymerisates being in the form of interpenetrating networks; to membranes and unsupported films prepared from the polymerisates; to carrier materials coated with the compositions and polymerisates; to optical sensors prepared from the polymerisates; and to methods of determining ions and/or gases in solutions and/or blood.

The present invention relates to a composition comprising (a) at leastone olefinic monomer (A), (b) a polymer of an olefinic monomer, (c) anindicator dye to the basic structure of which an olefinic polymerisablegroup is covalently bonded directly or via a bridge group, (d) at leastone at least diolefinic cross-linking agent, and (e) at least onepolymerisation initiator; to polymers from that composition; to amaterial coated with the polymer; and to the use thereof.

WO 88/05533 describes sensor membranes that can be copolymerisates ofvinylically substituted dye indicators and acrylamides ormethacrylamides. The copolymerisates are produced directly on an opticalcarrier material, for example a glass fibre, for example by dipping aglass fibre into the mixture of monomers, removing the glass fibre andthen polymerising the layer. The surface of the glass fibre isfunctionalised beforehand with acrylamides, so that the polymer islikewise covalently bonded to the surface. Membranes on which a dyeindicator has been immobilised are obtained from which it is virtuallyimpossible for the polymer-bonded dye to be washed out. A disadvantageof the described membranes is especially that their layer thicknessesare dependent upon the composition chosen/the viscosity thereof andcannot be controlled in a targeted manner, which has a direct adverseeffect on the response times and sensitivities. Usable membranes aretherefore obtainable only by chance depending upon the consistency ofthe monomers chosen.

WO 93/07483 describes sensors for indicating pH value in which theindicator dye is covalently bonded to the hydrophilic polymer membranein order to prevent it from being washed out through use. Theimmobilisation is carried out by subsequent treatment of the membranewith a dissolved dye indicator containing functional groups that arecapable of reacting with functional groups of the polymer membrane.Furthermore, only certain pre-prepared polymers can be used for amembrane, the mechanical and physical properties of which cannot beselectively adapted to the intended use. The manufacturing process is byits nature associated with a high degree of variation in product quality(for example in the content of dye indicator) which renders continuousproduction and application in standard systems difficult or impossible.

Analytica Chimica Acta, 276 (1993), 347-352 discloses an electrochemicalsensor which contains on a measuring electrode an ion-sensitive membranewhich consists of a cross-linked methacrylate polymer obtained in thepresence of polyvinylpyrrolidone. There is no mention of the propertiesfor an optical ion sensor and for this measuring method immobilisationwith a dye indicator is not required and is not described.

It has now been found, surprisingly, that polymers of hydrophilicolefinic monomers (A) containing a homo- or co-polymer of the samemonomer (A) or of hydrophilic monomer(s) (B) different from (A) and anolefinically substituted dye indicator are excellently suitable asmembranes for optical sensors for the determination of ions or gases,for example oxygen or carbon dioxide. The membranes have excellentmechanical strength and the dye indicator is covalently bonded to thepolymer spine and therefore cannot be washed out by the measuringsolution, which in total ensures a long usable life. The membranesexhibit the necessary optical transparency as a result of an unexpectedhomogeneous consistency. The desired degree of hydrophilicity can beadjusted in a targeted manner so that, especially for optical pHdetection, the pH measuring range can be predetermined by the choice andamount of the hydrophilic monomers and polymers. A further greatadvantage is that economical production processes, for example spincasting processes, can be used for the coating of the carrier materials,since the viscosity of the polymerisable composition can be set andadapted to the process technology by the choice and amount of thehydrophilic polymer. In addition, ecologically favourable manufacturingprocesses for mass production are possible, since aqueous coatingsolutions can be used and the polymerisation can be carried out directlyon the carrier material. There is thereby obtained a high degree ofproduction conformity especially with regard to the layer thicknesses,even in the case of very thin layers, so that standard calibration isgenerally adequate and further calibration is unnecessary if the sensorsshould be replaced. Furthermore, it is possible to produce very thin butat the same time uniform layers. The polymerisable compositions haveadequate storage stability and can be marketed as such. Thepolymerisates from the compositions surprisingly form a network in whichthe polymer molecules of the monomers (A) are embedded or, as it were,penetrate the network. It is surprising that no segregation is observedbut that, on the contrary, there is uniform distribution of the polymermolecules, so that the polymerisate is a homogeneous material.

The invention relates to a composition comprising

(a) at least one olefinic monomer (A),

(b) at least one polymer of at least one olefinic monomer,

(c) an indicator dye to the basic structure of which an olefinicpolymerisable group is covalently bonded directly or via a bridge group,

(d) at least one at least diolefinic cross-linking agent, and

(e) an effective amount of a polymerisation initiator.

The desired properties of the membrane can be varied and set within awide range by the choice of the monomers (A) and the component (b)polymers and the combination thereof. For the optical detection of ionsor for pH measurements in aqueous media, hydrophilic membranes aregenerally preferred. The hydrophilic character can be set by the choiceand amount of hydrophilic monomers (A), optionally in admixture withhydrophobic monomers, and the quantity ratios thereof, and by the choiceand amount of the component (b) polymer and the hydrophilicity thereofwhich is determined by the content of hydrophilic and/or hydrophobicmonomers. In the optical detection of gases in media which may beliquid, for example blood, preference is generally given to hydrophobicmembranes that can be obtained and adjusted as above but usinghydrophobic monomers (A) and component (b) polymers. Hydrophilic andhydrophobic monomers and polymers may accordingly be combined as desiredwith other hydrophilic and/or hydrophobic monomers and polymers in orderto obtain the desired properties.

"Hydrophilic" may indicate a solubility in water of at least 1% byweight, preferably at least 10% by weight, especially at least 20% byweight, more especially at least 40% by weight and very especially atleast 50% by weight, the percentages being based on the solution.

The component (b) polymer may comprise at least one monomer identical to(A), at least one monomer (B) that is different from (A), or a mixtureof such monomers. In a preferred form the component (b) polymer iscomposed predominantly, and especially solely, of monomer (A).

The hydrophilic olefinic monomers (A) and/or (B) may be present in anamount of from 5 to 95% by weight, preferably from 10 to 90% by weight,especially from 10 to 80% by weight and more especially from 20 to 70%by weight, based on the composition. The same applies to hydrophobicmonomers or mixtures of hydrophobic and hydrophilic monomers.

The hydrophilic component b) homo- or co-polymers may be present in anamount of from 95 to 5% by weight, preferably from 90 to 10% by weight,especially from 90 to 20% by weight and more especially from 80 to 30%by weight, based on the composition. The same applies to hydrophobicpolymers or polymers composed of mixtures of hydrophobic and hydrophilicmonomers.

The indicator dye may be present in an amount of from 0.01 to 10% byweight, preferably from 0.1 to 5% by weight and especially from 0.5 to3% by weight.

The polymerisation initiator may be present in an amount of from 0.1 to20% by weight, preferably from 0.5 to 10% by weight and especially from1 to 8% by weight.

The composition according to the invention comprises a cross-linkingagent, for example in an amount of from 0.1 to 30% by weight, preferablyfrom 0.5 to 20% by weight, especially from 0.5 to 10% by weight and moreespecially from 0.5 to 5% by weight.

The numerical values of the percentages by weight always add up to 100%by weight.

The monomers (A) or (B) are preferably selected from the group ofolefins substituted by at least one hydrophilic radical. The hydrophilicradical(s) is/are selected especially, for example, from the groupconsisting of pyrrolidonyl, amino, primary amino, secondary amino,corresponding ammonium groups and hydroxy, each being bonded directly orvia a bridge group to the olefin group. The bridge groups may be--C(O)--, --C(O)--O-alkylene-, --C(O)--NH-alkylene-, --C(O)--O--(C₂ -C₆alkylene-O)₁ to 12 --C₂ -C₆ alkylene-, --C(O)--NH--(C₂ -C₆ alkylene-O)₁to 12 --C₂ -C₆ alkylene- or --O-alkylene-. Acidic hydrophilic groups,for example --C(O)OH, may also be present in the form of salts, forexample in the form of alkali metal or alkaline earth metal salts.

The hydrophilic monomers (A) or (B) may correspond, for example, toformula I

    R.sub.1 R.sub.2 C═CR.sub.3 --Z                         (I)

wherein R₁, R₂ and R₃ are each independently of the other hydrogen or ahydrophobic substituent, and Z is a hydrophilic radical.

A hydrophobic substituent may be, for example, C₁ -C₁₂ alkyl, preferablyC₁ -C₆ alkyl, C₁ -C₁₂ alkoxy, preferably C₁ -C₆ alkoxy, C₁ -C₁₂haloalkyl, preferably C₁ -C₆ haloalkyl, phenyl, halophenyl, for examplechlorophenyl, C₁ -C₄ alkylphenyl, C₁ -C₄ alkoxyphenyl, a carboxylic acidester group having a total of from 2 to 20 carbon atoms, --CN, F or Cl.

In a preferred form, in formula I R₁ and R₂ are hydrogen and R₃ ishydrogen or methyl.

The hydrophilic radical may be, for example, --OH, --O--(C₂ -C₁₂alkylene)--OH and preferably --O--(C₂ -C₆ alkylene)--OH, --C(O)--NH₂,--C(O)--NH--(C₂ -C₁₂ alkylene) --OH and preferably --C(O)--NH--(C₂ -C₆alkylene)--OH, --C(O)--N--(C₂ -C₁₂ alkylene)₂ --OH and preferably--C(O)--N--(C₂ -C₆ alkylene)₂ --OH, --C(O)--NH--C₁ -C₁₂ alkyl andpreferably --C(O)--NH--C₁ -C₆ alkyl, --C(O)--N--(C₁ -C₁₂ alkyl)₂ andpreferably --C(O)--N--(C₁ -C₆ alkyl)₂, pyrrolidonyl, --C(O)--NH--C₁ -C₁₂alkylene-NH₂ and preferably --C(O)--NH--C₁ -C₆ alkylene-NH₂,--C(O)--NH--C₁ -C₁₂ alkylene-NH--C₁ -C₆ alkyl and preferably--C(O)--NH--C₂ -C₆ alkylene-NH--C₁ -C₄ alkyl, --C(O)--NH--C₁ -C₁₂alkylene-N--(C₁ -C₆ alkyl)₂ and preferably --C(O)--NH--C₂ -C₆alkylene-N--(C₁ -C₄ alkyl)₂, or --C(O)--O--(C₂ -C₁₂ alkylene)--OH andpreferably --C(O)--O--(C₂ -C₆ alkylene)--OH, or --C(O)--O--(C₂ -C₆alkylene-O)₁ to 12 --C₂ -C₆ alkylene-OH or --C(O)--NH--(C₂ -C₆alkylene-O)₁ to 12 --C₂ -C₆ alkylene-OH having the same or differentalkylene --O-- radicals which are preferably present from 1 to6,especially from 1 to 4, times, and alkylene is preferably ethylene,1,2- or 1,3-propylene or 1,4-butylene.

Some examples of those monomers A are vinyl alcohol, hydroxy-C₂ -C₆alkylvinyl ethers, acrylamide, methacrylamide, methyl acrylamide, methylmethacrylamide, ethyl acrylamide, ethyl methacrylamide, n- or iso-propylacrylamide, n- or iso-propyl methacrylamide, n-, iso- or tert-butylacrylamide, n-, iso- or tert-butyl methacrylamide, dimethyl acrylamide,dimethyl methacrylamide, diethyl acrylamide, diethyl methacrylamide,di-n- or di-iso-propyl acrylamide, di-n- or di-iso-propylmethacrylamide, di-n-, di-iso- or di-tert-butyl acrylamide, di-n-,di-iso- or di-tert-butyl methacrylamide, pyrrolidone, hydroxyethylacrylate and methacrylate, hydroxy-1,2-propyl acryl ate andmethacrylate, hydroxy-1,3-propyl acrylate and methacrylate,hydroxy-1,2-butyl acrylate and methacrylate, hydroxy-1,3-butyl acrylateand methacrylate, hydroxy-1,4-butyl acrylate and methacrylate,hydroxy-1,2-pentyl acrylate and methacrylate, hydroxy-1,3-pentylacrylate and methacrylate, hydroxy-1,4-pentyl acrylate and methacrylate,hydroxy-1,5-pentyl acrylate and methacrylate, hydroxy-1,2-hexyl acrylateand methacrylate, hydroxy-1,3-hexyl acrylate and methacrylate,hydroxy-1,4-hexyl acrylate and methacrylate, hydroxy- 1,5-hexyl acrylateand methacrylate, hydroxyethyl acrylamide and methacrylamide,hydroxy-1,2-propyl acrylamide and methacrylamide, hydroxy-1,3-propylacrylamide and methacrylamide, hydroxy-1,2-butyl acrylamide andmethacrylamide, hydroxy-1,3-butyl acrylamide and methacrylamide,hydroxy- 1,4-butyl acrylamide and methacrylamide, hydroxy-1,2-pentylacrylamide and methacrylamide, hydroxy-1,3-pentyl acrylamide andmethacrylamide, hydroxy-1,4-pentyl acrylamide and methacrylamide,hydroxy-1,5-pentyl acrylamide and methacrylamide, hydroxy-1,2-hexylacrylamide and methacrylamide, hydroxy-1,3-hexyl acrylamide andmethacrylamide, hydroxy-1,4-hexyl acrylamide and methacrylamide,hydroxy-1,5-hexyl acrylamide and methacrylamide, hydroxy-1,6-hexylacrylamide and methacrylamide, hydroxypolyoxyalkylene vinyl ethers,hydroxypolyoxyalkylene acrylate or methacrylate.

The component (b) polymer preferably comprises at least one identicalmonomer (A) of component (a) or a monomer (B) different from monomer(A), or a mixture of those monomers. In the case of a copolymer, thepolymer comprises different monomers (A), or monomers (A) and monomers(B). Homopolymers are composed of monomers (A) or of monomers (B). In apreferred form of the composition according to the invention thecomponent (b) polymer is composed of a monomer (A) selected from thesame group of monomers (A) and is the same or different, the groupbeing, for example, acrylates and/or methacrylates, acrylamides and/ormethacrylamides, vinyl alcohols and/or hydroxyalkyl vinyl ethers,pyrrolidone and styrene. In an especially preferred form of thecomposition according to the invention the component (b) polymer iscomposed of the same monomer (A) as that used as monomer (A).

Some especially preferred combinations of hydrophilic monomers andpolymers are vinyl pyrrolidone/pyrrolidone, acrylamide/polyacrylamide,acrylamide/polymethacrylamide, methacrylamide/polyacrylamide, ethylacrylamide/polyethyl acrylamide, propyl acrylamide/polypropylacrylamide, tert-butyl acrylamide/poly-tert-butyl acrylamide, tert-butylacrylamide/polyacrylamide, tert-butyl acrylamide/polymethacrylamide,hydroxyalkyl vinyl ether/polyhydroxyalkyl vinyl ether, hydroxyethylmethacrylate/polyhydroxyethyl methacrylate, hydroxyethylmethacrylate/polyhydroxyethyl acrylate, hydroxy-n-propylmethacrylate/polyhydroxy-n-propyl methacrylate, hydroxy-isopropylmethacrylate/polyhydroxy-isopropyl methacrylate, hydroxy-n-butylmethacrylate/polyhydroxy-n-butyl methacrylate, hydroxy-n-pentylmethacrylate/polyhydroxy-n-pentyl methacrylate, hydroxy-n-hexylmethacrylate/polyhydroxy-n-hexyl methacrylate.

The hydrophobic monomers (A) or (B) may correspond, for example, toformula III

    R.sub.6 R.sub.7 C=CR.sub.8 -Y                              (III)

wherein

R₆, R₇ and R₈ are each independently of the other hydrogen or ahydrophobic substituent, and Y is a hydrophobic radical.

The hydrophobic substituents may be, for example, C₁ -C₁₂ alkyl,preferably C₁ -C₆ alkyl, C₁ -C₁₂ alkoxy, preferably C₁ -C₆ alkoxy, C₁C₁₂ haloalkyl, preferably C₁ -C₆ haloalkyl, phenyl, halophenyl, forexample chlorophenyl, C₁ -C₄ alkylphenyl, C₁ -C₄ alkoxyphenyl, acarboxylic acid ester group having a total of from 2 to 20 carbon atoms,--CN, F or Cl.

The hydrophobic radical Y may be a radical as mentioned for R₆ to R₈.Preferred radicals Y are C₁ -C₆ alkyl, C₁ -C₆ alkoxy, phenyl,chlorophenyl, C₁ -C₄ alkylphenyl, C₁ -C₄ alkoxyphenyl, carboxylic acidester groups having a total of from 2 to 10 carbon atoms, --CN and Cl.

In a preferred form, in formula III R₆ and R₇ are hydrogen and R₈ ishydrogen or methyl.

Some preferred combinations of hydrophobic monomers and polymers arestyrene/polystyrene, methyl acrylate/polymethyl acrylate, methylmethacrylate/polymethyl methacrylate, vinyl ethyl ether/polyvinyl ethylether, acrylonitrile/polyacrylonitrile and acrylonitrile/polystyrene.

The component (b) polymer may have a mean molecular weight of from 1000to 1 000 000 daltons, preferably from 10 000 to 500 000 daltons,determined in accordance with the gel permeation method using standardpolymers of known molecular weight.

The indicator dye is preferably a fluorophore for the detection ofchanges in emissions, for example fluorescence.

The indicator dye may be a dye of formula II

    R.sub.4 HC═CR.sub.5 --(X).sub.q --dye                  (II)

wherein

R₄ is methyl and R₅ is hydrogen, or

R₅ is methyl and R₄ is hydrogen,

q is 0 or 1,

X is a bridge group, and

dye is the monovalent radical of a dye indicator.

In a preferred form, R₄ is hydrogen and R₅ is hydrogen or methyl.

In a different preferred form, q is 1.

The bridge group X may be, for example, --O--, --NH, --NH--C₁ -C₄ alkyl,--C(O)--O--, --C(O)--NH--, --C(O)--NH--C₁ -C₄ alkyl-, --NH--(CO)--O--,--O--C(O)--NH--, --C(O)--O--C₂ -C₁₂ alkylene-O--C(O)--, --C(O)--NH--C₂-C₁₂ alkylene--O--C(O)--, --C(O)--O--C₂ -C₁₂ alkylene-NH--C(O)--,--C(O)--NH--C₂ -C₁₂ alkylene-NH--C(O)--, --C(O)--NH--C₂ -C₁₂alkylene-C(O)--NH--, --NH--C(O)--O--C₂ -C₁₂ alkylene-O--C(O)--,--C(O)--O--(C₂ -C₆ alkylene-O)₁ to 12 --, --C(O)--O--(C₂ -C₆ alkylene-O)₁ to 12 --C₂ -C₆ alkylene-NH--, --C(O)--NH--(C₂ -C₆ alkylene-O)₁ to 12--C₂ -C₆ alkylene-NH--, --C(O)--NH--(C₂ -C₆ alkylene-O)₁ to 12 --CH₂--C(O)--NH--.

Preferred bridge groups are --C(O)--NH--, --C(O)--O--(CH₂ CH₂ --O)₁ to 6--, --C(O)--NH--(CH₂ CH₂ --O)₁ to 6 --CH₂ C(O)--NH--, --C(O)--NH--(C₂-C₆ alkylene-O)₁ to 6 --C₂ -C₆ alkylene-NH-- and --C(O)--NH--C₂ -C₁₂alkylene-C(O)--NH--.

The dye indicator may be a dye indicator that changes its absorption oremission under the action of a test sample and thus produces ameasurable signal. Especially preferred are fluorescent dyes(fluorophores), for example those of the group of xanthenes andbenzoxanthenes (for example fluorescein, halogenated fluoresceins,seminaphthofluoresceins, seminaphthorhodafluores, 2,3-benzfluorescein,3,4-benzfluorescein, the isomers of benzrhodamine and substitutedderivatives, the isomers of benzchromogene and substituted derivatives);acridines (for example acridine, 9-amino-6-chloroacridine); acridones(for example 7-hydroxyacridone, 7-hydroxybenzacridone); pyrenes (forexample 8-hydroxypyrene-1,3,6-trisulfonic acid); coumarins (for example7-hydroxycoumarin, 4-chloromethyl-7-hydroxycoumarin); conjugated cyaninedyes and metal complexes, for example platinum porphyrins. Thefluorescent dyes are olefinically functionalised for bonding to apolymer.

Especially preferred fluorophores are 3- or 4-acryloylaminofluoresceinand 3- or 4-methacryloylaminofluorescein.

A wide variety of absorption dyes for sensors is known. Examples aremethyl violet, crystal violet, malachite green oxalate, methyl green,quinaldine red, 4-phenylazodiphenylamine, thymol blue(thymolsulfonephthalein), metacresol purple, orange IV, benzopurpurine4B, N,N-dimethyl-p-(m-tolylazo)amine, bromophenol blue, congo red,methyl orange, bromocresol green, resazurin,4-phenylazo-1-naphthylamine, ethyl red, lacmoid, alizarine red S,bromocresol purple, chlorophenol red, alizarine, bromothymol blue,brilliant yellow, phenol red, neutral red, cresol red, metacresolpurple, thymol blue, o-cresolphthalein, p-naphtholbenzein,phenolphthalein, thymolphthalein, alizarine yellow R, curcumin,alizarine. The absorption dyes are olefinically functionalised forbonding to a polymer.

Suitable functional groups for bonding to a carbon atom of the olefinicgroup (directly or via a bridge group) are, for example, --OH, --NH₂,--NH--C₁ -C₄ alkyl, --C(O)OH, --C(O)Cl, --SO₂ Cl, --C(O)--NH₂,--C(O)--NH--CH₂ CH₂ --OH, --C(O)--O--CH₂ CH₂ --OH, --C(O)--NH--CH₂ CH₂--NH₂, --C(O)--O--CH₂ CH₂ --NH₂, --NH--C(O)--CH₂ OH, --CH₂ I, --CH₂ Br,--CH₂ Cl, --NCS, --NCO, --N₃ and succinyl esters. Vinyl or methylvinylis suitable for direct bonding. The indicator dye may also be bondeddirectly or via a bridge group to the nitrogen atom of an unsubstitutedor substituted maleinimidyl group.

Suitable cross-linking agents are, for example, acrylic or methacrylicacid esters or amides of polyols, preferably diols to tetrols, orpolyamines, preferably diamines to tetramines. Aliphatic andcycloaliphatic diols and diamines are preferred. Such cross-linkingagents are known and many are described in the literature. Some examplesof polyols are alkylene diols, such as ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyalkylene diols ofpreferably C₂ -C₆ alkylene diols having especially from 3 to 100alkylene diol units, for example polyethylene glycols, polypropyleneglycols, polybutylene glycols and polyethylene-propylene glycols,1,1,1-trihydroxymethyl-ethane or -propane, pentaerythritol anddipentaerythritol. Some examples of polyamines are ethylenediamine,1,3-propanediamine, 1,4-butanediamine, 1,6-hexanediamine,diethylenetriamine and triethylenetetramine. Other known cross-linkingagents are, for example, divinylbenzene andbis(dimethylmaleinimidyl)alkylenes, for example methylene or1,2-ethylene-bis(dimethylmaleinimidyl).

Some examples are N,N'-methylene-bis-acrylic acid amide,N,N'-ethylene-bis-acrylic acid amide, N,N'-propylene-bis-acrylic acidamide, ethylene glycol bismethacrylate, propylene glycolbismethacrylate, butylene glycol bismethacrylate, hexylene glycolbismethacrylate and polyethylene glycol bismethacrylates of polyethyleneglycols having mean molecular weights of from 200 to 3000.

The composition according to the invention comprises polymerisationinitiators which can be activated either thermally or by the action ofradiation. Examples of thermal initiators are radical formers, forexample organic azo compounds, peroxo compounds and peroxodisulfates.Some examples are α,α'-azo-bisisobutyronitrile or ammoniumperoxodisulfate. Examples of photoinitiators that can be activated byradiation, for example UV light, which can optionally be used togetherwith sensitisers, are benzophenones, xanthones, thioxanthones,α-sec-amino-acetophenones and α-hydroxy-acetophenones.

The components of the composition according to the invention are knownor can be prepared in accordance with known or analogous processes.Functionalised indicator dyes are known or can be prepared andderivatised with reagents that form bridge groups in accordance withknown or analogous processes. Aminofluorescein acrylamide iscommercially available. Rhodamines derivatised with carboxyalkyl groupsare described, for example, by T. Werner et al. in Journal ofFluorescence, Vol. 2, No. 2, pages 93 to 98 (1992). The carboxy groupsmay, if desired, he functionally derivatised in known manner (amides,amines etc.). The composition according to the invention may compriseadditives for improving processability, for example flow agents,viscosity-increasing or viscosity-reducing agents and solvents.

It is generally advantageous, however, to add a solvent or diluent or amixture of solvents. Polar and, optionally, protic solvents arepreferred. Examples of such solvents and diluents that may be mentionedare: water; esters, such as ethyl acetate; ethers, such as diethylether, dipropyl ether, diisopropyl ether, dibutyl ether, tert-butylmethyl ether, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol dimethyl ether, dimethoxy-diethylether, tetrahydrofuran or dioxane; ketones, such as acetone, methylethyl ketone or methyl isobutyl ketone; alcohols, such as methanol,ethanol, propanol, isopropanol, butanol, ethylene glycol or glycerol;amides, such as N,N-dimethylformamide, N,N-diethylformamide,N,N-dimethylacetamide, N-methylpyrrolidone or hexamethylphosphoric acidtriamide; nitriles, such as acetonitrile or propionitrile; andsulfoxides, such as dimethyl sulfoxide. Preferred solvents are water,alkanols and N-dialkylated carboxylic acid amides.

The composition according to the invention is excellently suitable forthe coating of carrier materials, especially carriers which may betransparent, in accordance with customary surface-coating methods, thelayer being polymerised in a manner known per se after the coating andwhere appropriate after removal of a co-used solvent. The coatedmaterial is especially suitable for the manufacture of sensors. Thecomposition according to the invention is excellently suitable for themanufacture of membranes for optical sensors.

The invention relates also to a method of coating carrier materialswherein the composition according to the invention is applied to atleast one surface of the carrier material, where appropriate a solventis removed, and the layer is polymerised.

For the purpose of improving adhesion the carrier materials may betreated beforehand with adhesion promoters. For the same purpose it isalso possible to carry out plasma treatment of the carrier material inorder to generate functional groups on the surface. The surface may alsobe provided with copolymerisable groups in order to achieve anespecially high degree of adhesion. Known adhesion promoters for glassare, for example, triethoxy-glycidyloxy-silane,3-azidopropyl-triethoxysilane or 3-aminopropyl-triethoxysilane. Thesurfaces so treated can be further modified, for example withO-(N-succinimidyl)-6-(4'-azido-2'-nitrophenylamino)-hexanoate. It hasproved especially advantageous to treat the surfaces with silanes ofethylenically unsaturated carboxylic acid esters, for examplemethacrylic acid 3-trimethoxysilyipropyl ester, because in thepolymerisation the layer can be anchored covalently to the surface.Known coating techniques are, for example, spreading, immersion, knifeapplication, spraying, casting, curtain casting or, especially, spincasting or spin coating respectively. It is especially advantageous thatthe coating itself can be effected with aqueous solutions and in thiscase too spin coating processes can be used.

The invention relates also to a carrier material wherein a layer of thecomposition according to the invention has been applied to at least onesurface.

The invention relates also to a carrier material wherein a polymer layerof the composition according to the invention has been applied to atleast one surface. The polymer layers are optically transparent and aretherefore especially suitable for optical detection methods.

The invention relates also to an optical sensor wherein a polymer layerof the composition according to the invention has been applied to atleast one surface. In this form of the invention there is preferably noproton-sensitive fluorophore for pH detection present in a hydrophilicpolymer layer.

The invention relates also to the use of the sensors according to theinvention for the optical determination of ions and gases (for exampleO₂ or CO₂ in blood). In this form of the invention there is preferablyno proton-sensitive fluorophore for pH detection present in thehydrophilic polymer layer.

The invention relates also to a polymer from a composition according tothe invention, preferably in the form of an unsupported film which canbe used directly as an optical sensor. The polymers may be obtained, forexample, by detaching the layers from the carrier material or by meansof polymerisation in moulds.

The geometric shape of the carrier material may vary to a very greatextent; for example, it may be in the form of fibres, cylinders,spheres, cuboids or cubes. Also possible are throughflow systems inwhich continuous measurements or successive measurements can be made.Planar sensors are preferred. The carrier material is preferablytransparent. It may be, for example, inorganic glass or transparentplastics, such as polycarbonate, polyesters, polyamides or polyacrylatesor polymethacrylates. In another preferred form the carrier material ofthe optical sensors is transparent and preferably consists of glass or atransparent polymer.

The planar sensor may have any desired external shape, for example itmay be square, rectangular or round. It may have a surface area of from0.01 to approximately 50 cm², advantageously from 0.02 to 10 cm². Themeasuring region of the sensor may have an area of, for example, lessthan 5 mm², preferably less than or equal to 2 mm². The measuring regioncan be identical with a fully coated surface of the sensor.Advantageously a coating provided on both sides but locally separatedcan be used.

The thickness of polymer layer (b) may be, for example, from 0.01 to 50μm, preferably from 0.1 to 25 μm and especially from 0.1 to 10 μm.

The forms of the invention mentioned above are subject to the samepreferences as those indicated for the composition according to theinvention.

The polymerisation of the composition according to the invention can becarried out using thermal initiators at elevated temperature, forexample from 40° to 200° C. and preferably from 50° to 150° C. Thephotopolymerisation can be carried out at room temperature. In that casean increase in temperature as mentioned earlier can be used toaccelerate the reaction. The polymers may also be prepared by plasmapolymerisation.

For the determination of cations and anions there are generally alsoincorporated ionophores which on contact with the analysis solutionproduce as a result of interaction with the indicator dye a change inthe absorption or emission in the form of a measurable signal, thusallowing optical determination. As a rule in such systems, salts, suchas tetraphenyl borate, and optionally buffers are also used. If theindicator dye is proton-sensitive, that sensitivity can be utiliseddirectly for the determination of the pH value or indirectly inpH-altering reactions for the determination of ions (anions or metalcations). The determination of potassium is described, for example, byT. Werner et al. in Journal of Fluorescence, Vol. 2, No. 2, pages 93 to98 (1992) and can be carried out analogously to that process. The pHdetermination using two sensors having different dependencies on theionic strength of the measuring solution is described in DE-A-3 430 935and can be carried out analogously using the sensors according to theinvention. The radiation used for measurement may be selected from theUV range by way of the visible range to the near IR range (NIR range);the choice is substantially dependent upon the nature of the dyeindicator.

The hydrophilic polymer membranes prepared according to the inventionare especially suitable for the optical detection of the pH value inaqueous electrolyte solutions in the physiological range, for example inblood or blood serum, if a proton-sensitive fluorophore is present inthe membrane.

The method for the independent, reversible, optical determination of thepH value and the ionic strength of an aqueous sample (electrolytesolution) with the aid of two different sensors in accordance with thefluorescence method can be carried out, for example, as follows: twooptical sensors, which are each composed of polymers of differentstructure but each contain the same fluorescent dye and which eachconsist of a coated material according to the invention, are broughtinto contact with an aqueous test sample and irradiated with excitinglight, the fluorescence is measured and the pH values and the ionicstrengths are calculated from the measured fluorescence intensities withreference to calibration curves.

In detail, a procedure may be carried out in which, after calibrationwith samples of known ionic strength and known pH, the fluorescenceintensity in contact with an electrolyte solution of unknown compositionis measured and the separate contributions of the ionic strength and thepH to the measured fluorescence intensity are determined by calculation.The measurement data obtained from the calibrations are evaluated bycalculation, for example using a pattern recognition algorithm. Usingthe calculation method the pH and the ionic strength can then bedetermined from the measurement data obtained. Both precalibration anddirect calibration can be carried out.

The sensors are brought into contact with the calibration solutions orwith the test samples. This can be done by hand (for example usingpipettes) or with a suitable automatic throughflow system, the sensorsbeing rigidly mounted in a flow cell. Such throughflow cells are knownto the person skilled in the art and they can be simply adapted to theparticular intended use.

As light sources for exciting the fluorescence it is possible to use UVlamps (for example mercury vapour lamps, halogen lamps), lasers, diodelasers and light-emitting diodes. It may be advantageous to use filtersto filter out light of the wavelength at which the fluorescent dye hasan absorption maximum. The fluorescent light emitted by the sensors canbe collected, for example using a lens system, and then guided to adetector, for example a secondary electron multiplier or a photodiode.The lens system can be so arranged that the fluorescence radiationthrough the transparent carrier, over the edges of the carrier orthrough the analysis sample is measured. Advantageously the radiation isguided in a manner known per se via a dichroic mirror. The fluorescenceof the sensors is preferably measured while in contact with thecalibration or sample solutions.

An example of the procedure for the measuring method is described in theExamples.

The following Examples illustrate the invention.

A) PREPARATION EXAMPLES Examples A1 to A9: Preparation of coatedcarriers (sensors)

Example A1:

Glass substrates (plates of 18 mm diameter) are first cleaned with 30%sodium hydroxide solution and then activated in 65% nitric acid. Theactivated plates are then silanised with methacrylic acid3-trimethoxysilylpropyl ester. 150 μl of hydroxyethyl methacrylate, 5 mgof N,N-methylenebisacrylic acid amide, 2 mg of4-acryloylaminofluorescein and 20 mg of ammonium peroxodisulfate areadded to 4 ml of solution taken from a stock solution of 4 g ofpolyhydroxyethyl methacrylate in 60 ml of dimethylformamide. 50 μl ofthe resulting mixture are transferred by pipette to a plate lying on thehead of a spin coater and the plate is spun for 30 seconds at a speed of5000 revolutions per minute. For polymerisation the coated plates arethen kept in an oven at 64° for 2 to 3 hours. Transparent substrateshaving a polymer layer of about 1 μm thickness are obtained. The polymerlayer has good mechanical stability.

Example A2:

Glass substrates (plates of 18 mm diameter) are first cleaned with 30%sodium hydroxide solution and then activated in 65% nitric acid. Theactivated plates are then silanised with methacrylic acid3-trimethoxysilylpropyl ester. 150 μl of hydroxyethyl methacrylate, 5 mgof N,N-methylenebisacrylic acid amide, 2 mg of4-acryloylaminofluorescein and 10 mg of Irgacure 651® (photoinitiator,Ciba-Geigy AG) are added to 4 ml of solution taken from a stock solutionof 4 g of polyhydroxyethyl methacrylate in 60 ml of dimethylformamide.50 μl of the resulting mixture are transferred by pipette to a platelying on the head of a spin coater and the plate is spun for 30 secondsat a speed of 5000 revolutions per minute. For polymerisation the coatedplates are then irradiated with UV light (365 nm, 1300 μW/cm²) for 10 to20 minutes at room temperature. Transparent substrates having a polymerlayer of about 1 μm thickness are obtained. The polymer layer has goodmechanical stability.

Examples A3 to A7:

In a manner analogous to that described in Examples A1 and A2 it is alsopossible to prepare the other membranes listed in Table 1.

                  TABLE 1                                                         ______________________________________                                                                              mg cross-                                                                mg   linking                                                                              mg                               polymer.sup.1                                                                        mg     sol    monomer.sup.2                                                                        μl                                                                              dye.sup.3                                                                          agent.sup.4                                                                          initiator                        ______________________________________                                        PVP    600    DMF    VP     300  4    10     40.sup.5                         PVP    600    DMF    VP     300  4    10     20.sup.6                         PAA    800    H.sub.2 O                                                                            AA     150  2     5     20.sup.5                         PHEMA  270    DMF    HEMA   150  2     5     20.sup.5                         PHEMA  270    DMF    HEMA   150  2     5     10.sup.6                         PHPMA  1600   DMF    HPMA   300  4    10     40.sup.5                         PHBA   670    DMF    HBA    300  4    10     40.sup.5                         ______________________________________                                         .sup.1 PVP: polyvinylpyrrolidone, PAA: polyacrylamide, PHEMA:                 polyhydroxyethyl methacrylate, PHPMA: polyhydroxypropyl methacrylate,         PHBA: polyhydroxybutyl acrylate                                               .sup.2 VP: vinylpyrrolidone, AA: acrylamide, HEMA: hydroxyethyl               methacrylate, HPMA: hydroxypropyl methacrylate, HBA: hydroxybutyl acrylat     .sup.3 4acryloylaminofluorescein                                              .sup.4 N,Nmethylenebisacrylic acid amide                                      .sup.5 ammonium peroxodisulfate                                               .sup.6 Irgacure ® 651                                                     sol = solvent                                                                 DMF = dimethylformamide                                                  

B) APPLICATION EXAMPLES

Examples B1 to B8:

Two sensors are mounted one behind the other in two flow cells. Thecalibration solutions or sample solutions are metered and conveyedthrough the cells using pumps. The measuring arrangement isthermostatically controlled. The light of a halogen lamp (white light,excitation wavelength is 480 nm) is passed through an excitation filter,reflected on a dichroic mirror and focussed onto the planar sensorsusing lenses. The fluorescent light (at 520 nm) emitted by the sensorsis collected using the same lens system and guided by the dichroicmirror via an emission filter to a photodiode. The fluorescence of thesensors is recorded while being acted upon by the calibration or samplesolutions. The measurement data obtained from the calibrations areevaluated with a partial least squares pattern recognition algorithm;the calculation method is then capable of determining the pH and theionic strength from the measurement data obtained from the sample.

The following Tables give the effects of the different membranecompositions on the properties of the embedded fluorescent dyes. Sincethe variation in the ionic strength alters not only the pK_(a) of thedye but also the pH of the measuring solution, and the latter in turninfluences the maximum fluorescence intensity of the dye, in order tomeasure the pH using the described sensor system it is necessary for theionic strength dependency both of the pK_(a) of the dye and of the pH ofthe calibration buffer solution to be known. Table 2 shows examples offluorescent dyes, their pK_(a), and the ionic strength dependency of thepK_(a) and of the pH with different sensor membrane compositions.Sensors from the following Table having different ionic strengthdependencies can be selected for pH determination.

                  TABLE 2                                                         ______________________________________                                                                 ionic strength                                                                         buffer curve                                polymer.sup.1                                                                          dye.sup.2                                                                            pK.sub.a.sup.3                                                                         dependency.sup.4                                                                       displacement.sup.5                          ______________________________________                                        PVP      A      6.3      0.02     0.02                                        PAA      A      6.4      0.13     0.10                                        PHEMA    A      7.0      0.28     0.25                                        PHBA     A      7.3      0.05     0.10                                        PVP      B      6.6      0.02     0.02                                        PAA      B      6.7      0.16     0.10                                        PHEMA    B      7.3      0.30     0.20                                        PHPMA    B      7.4      0.13     0.10                                        ______________________________________                                         .sup.1 for abbreviations see Table 1                                          .sup.2 A: 4acryloylaminofluorescein, B:                                       4acryloylamino-4',5dimethylfluorescein                                        .sup.3 at 0.1M ionic strength                                                 .sup.4 pK.sub.a displacement between the calibration curves in buffer         solutions of 0.1M and 0.3M ionic strength                                     .sup.5 pH displacement between the calibration curves in buffer solution      of 0.1M and 0.3M ionic strength                                          

What is claimed is:
 1. A composition, comprising:(a) at least oneolefinic monomer (A), (b) at least one polymer prepared from at leastone olefinic monomer, (c) an indicator dye to the basic structure ofwhich an olefinic polymerisable group is covalently bonded directly orvia a bridge group, (d) at least one diolefinic cross-linking agent; and(e) an effective amount of a polymerisation initiator, characterized inthat upon polymerisation of the composition a polymerisate is preparedin the form of an interpenetrating network.
 2. A composition accordingto claim 1, wherein the monomers and polymers are hydrophilic and have asolubility in water of at least 1% by weight.
 3. A composition accordingto claim 1, wherein the component (b) polymer is prepared from at leastone monomer identical to (A), at least one monomer (B) that is differentfrom (A), or a mixture of such monomers.
 4. A composition according toclaim 3, wherein the component (b) polymer is prepared predominantly orsolely from monomer (A).
 5. A composition according to claim 3, whereinthe olefinic monomer(s) (A) and/or (B) are present in an amount of from5 to 95% by weight, based on the composition.
 6. A composition accordingto claim 1, wherein the component (b) polymers are present in an amountof from 95 to 5% by weight, based on the composition.
 7. A compositionaccording to claim 1, wherein the indicator dye is present in an amountof from 0.01 to 10% by weight.
 8. A composition according to claim 1,wherein the polymerisation initiator is present in an amount of from 0.1to 20% by weight.
 9. A composition according to claim 1, wherein thecross-linking agent is present in an amount of from 0.1 to 30% byweight.
 10. A composition according to claim 3, wherein the monomers (A)or (B) are selected from the group of olefins substituted by at leastone hydrophilic radical.
 11. A composition according to claim 10,wherein the hydrophilic radical(s) is/are selected from the grouppyrrolidonyl, amino, primary amino, secondary amino, ammonium groups andhydroxy, each being bonded directly or via a bridge group to the olefingroup.
 12. A composition according to claim 11, wherein the bridge groupis --C(O)--, --C(O)--O-alkylene-, --C(O)--NH-alkylene-, --C(O)--O--(C₂-C₆ alkylene-O)₁ to 12 --C₂ -C₆ alkylene-, --C(O)--NH--(C₂ -C₆alkylene-O)₁ to 12 --C₂ -C₆ alkylene- or --O-alkylene-.
 13. Acomposition according to claim 10, wherein the monomers (A) or (B)correspond to formula I

    R.sub.1 R.sub.2 C═CR.sub.3 --Z                         (I)

wherein R₁, R₂ and R₃ are each independently of the other hydrogen or ahydrophobic substituent, and Z is a hydrophilic radical.
 14. Acomposition according to claim 13, wherein the hydrophobicsubstituent(s) is/are selected from C₁ -C₁₂ alkyl, C₁ -C₁₂ alkoxy, C₁-C₁₂ haloalkyl, phenyl, halophenyl, C₁ -C₄ -alkylphenyl, C₁ -C₄alkoxyphenyl, carboxylic acid ester groups having a total of from 2 to20 carbon atoms, --CN, F and Cl.
 15. A composition according to claim13, wherein in formula I R₁ and R₂ are hydrogen and R₃ is hydrogen ormethyl.
 16. A composition according to claim 13, wherein the hydrophilicradical is --OH, --O--(C₂ -C₁₂ alkylene)--OH, --C(O)--NH₂,--C(O)--NH--(C₂ -C₁₂ alkylene)--OH, --C(O)--N--(C₂ -C₁₂ alkylene)₂ --OH,--C(O)--NH--C₁ -C₁₂ alkyl, --C(O)--N--(C₁ -C₁₂ alkyl)₂, pyrrolidonyl,--C(O)--NH--C₁ -C₁₂ alkylene-NH₂, --C(O)--NH--C₁ -C₁₂ alkylene-NH--C₁-C₆ alkyl, --C(O)--NH--C₁ -C₁₂ alkylene-N--(C₁ -C₆ alkyl)₂,--C(O)--O--(C₂ -C₁₂ alkylene)-OH, or --C(O)--O--(C₂ -C₆ alkylene-O)₁ to12 --C₂ -C₆ alkylene-OH or --C(O)--NH--(C₂ -C₆ alkylene-O)₁ to 12 --C₂-C₆ alkylene-OH having the same or different alkylene-O-- radicals. 17.A composition according to claim 1, wherein the component (b) polymer isprepared from the same monomer (A) as that used as monomer (A).
 18. Acomposition according to claim 1, wherein the component (b) polymer hasa mean molecular weight of from 1000 to 1 000
 000. 19. A compositionaccording to claim 1, wherein the indicator dye is a dye of formula II

    R.sub.4 HC═CR.sub.5 --(X).sub.q --dye                  (II)

wherein R₄ is methyl and R₅ is hydrogen, or R₅ is methyl and R₄ ishydrogen, q is 0 or 1, X is a bridge group, and dye is the monovalentradical of a dye indicator.
 20. A composition according to claim 19,wherein R₄ is hydrogen and R₅ is hydrogen or methyl.
 21. A compositionaccording to claim 19, wherein q is
 1. 22. A composition according toclaim 19, wherein the bridge group X is --O--, --NH, --NH--C₁ -C₄alkyl-, -C(O)-O-, -C(O)-NH-, -C(O)--NH--C₁ -C₄ alkyl-, --NH--(CO)--O--,--O--C(O)--NH--, --C(O)--O--C₂ -C₁₂ alkylene-O--C(O)--, --C(O)--NH--C₂-C₂ -C₁₂ alkylene-O--C(O)--, --C(O)--O--C₂ -C₁₂ alkylene-NH--C(O)--,--C(O)--NH--C₂ -C₁₂ alkylene-NH--C(O)--, --C(O)--NH--C₂ -C₁₂alkylene-C(O)--NH--, --NH--C(O)--O--C₂ -C₁₂ alkylene-O--C(O)--,--C(O)--O--(C₂ -C₆ alkylene-O)₁ to 12 --, --C(O)--O--(C₂ -C₆ alkylene-O)₁ to 12 --C₂ -C₆ alkylene-NH--, --C(O)--NH--(C₂ -C₆ alkylene-O)₁ to 12--C₂ -C₆ alkylene-NH-- or --C(O)--NH--((C₂ -C₆ alkylene-O)₁ to 12 --CH₂--C(O)--NH--.
 23. A composition according to claim 1, wherein thecross-linking agent is selected from the group consisting of acrylic andmethacrylic acid esters and amides of polyols and polyamines, divinylbenzene and bis(dimethylmaleinimidyl)alkylenes.
 24. A compositionaccording to claim 1, wherein the polymerisation initiator is an organicazo compound, peroxo compound, peroxodisulfate or a photoinitiator thatcan be activated by radiation.
 25. A composition according to claim 1,which comprises a solvent.
 26. A composition according to claim 3,wherein the hydrophobic monomers (A) or (B) correspond to formula I

    R.sub.1 R.sub.2 C═CR.sub.3 --Y                         (III)

wherein R₁, R₂ and R₃ are each independently of the other hydrogen or ahydrophobic substituent, and Y is a hydrophobic radical.
 27. Acomposition according to claim 26, wherein the hydrophobicsubstituent(s) is/are selected from C₁ -C₁₂ alkyl, C₁ -C₁₂ alkoxy, C₁-C₁₂ haloalkyl, phenyl, halophenyl, C₁ -C₄ -alkylphenyl, C₁ C₄alkoxyphenyl, carboxylic acid ester groups having a total of from 2 to20 carbon atoms, --CN, F and Cl.
 28. A composition according to claim26, wherein in formula III R₁ and R₂ are hydrogen and R₃ is hydrogen ormethyl.
 29. A composition according to claim 26, wherein in formula IIIY is C₁ -C₆ alkyl, C₁ -C₆ -alkoxy, phenyl, chlorophenyl, C₁ -C₄alkylphenyl, C₁ -C₄ alkoxyphenyl, a carboxylic acid ester group having atotal of from 2 to 10 carbon atoms, --CN or --Cl.
 30. A carriermaterial, comprising: a layer of the composition according to claim 1applied to at least one surface thereof, wherein the carrier material issuitable for use in the manufacture of optical sensors.
 31. A carriermaterial, comprising: a layer of a polymerisate prepared from thecomposition according to claim 1 applied to at least one surfacethereof, wherein the polymerisate is in the form of an interpenetratingnetwork.
 32. A carrier material according to claim 31 that is planar.33. A carrier material according to claim 31 that is transparent.
 34. Acarrier material according to claim 31 that consists of a glass or atransparent polymer.
 35. A carrier material according to claim 31,wherein the polymerisate layer has a thickness of from 0.01 to 50 μm.36. An optical sensor, comprising: a layer of a polymerisate preparedfrom the composition according to claim 1 applied to at least onesurface thereof, wherein the polymerisate is in the form of aninterpenetrating network.
 37. A method for the optical determination ofions or gases in a solution or blood, comprising:contacting the solutionor blood with an optical sensor comprising a polymerisate prepared fromthe composition according to claim 1, under conditions effective tocause a change in absorption or emission in the form of a measurablesignal, measuring the measurable signal; and determining the presenceand/or ionic strength of the ions or gases in the solution or blood bycomparing the measurable signal to calibrated standards.
 38. Apolymerisate prepared from a composition according to claim 1, whereinthe polymerisate is in the form of an unsupported film.
 39. Acomposition according to claim 1 wherein the polymerisate is suitablefor use in optical sensors.
 40. A carrier material according to claim 31wherein the polymerisate is suitable for use in optical sensors.
 41. Apolymerisate according to claim 38 wherein the unsupported film issuitable for use in optical sensors.
 42. A transparent membrane,comprising:a polymerisate of(a) at least one olefinic monomer (A), (b)at least one polymer prepared from at least one olefinic monomer, (c) anindicator dye to the basic structure of which an olefinic polymerisablegroup is covalently bonded directly or via a bridge group, (d) at leastone diolefinic cross-linking agent; and (e) an effective amount of apolymerisation initiator,wherein the polymerisate is in the form of aninterpenetrating network.
 43. A transparent membrane according to claim42 wherein the polymerisate is suitable for use in optical sensors.